Ornate Ceramic Prosthetic

Wondrous item, rare (requires attunement)
  Developed by a mysterious puppeteer, the painted patterns that decorate the ceramic surface of this appendage seem to shift from day to day, and vary in texture and hue from one individual to another. To attune to this item, you must attach it to the site of a severed arm, at which point the ceramic plating magically mobilises to form a copy of the lost limb. The prosthetic is a fully capable part of your body and can’t be removed against your will whilst your attunement to it persists.
  When performing unarmed strikes using this prosthetic, the ceramic plating on the side of your hand morphs into a sharp, ceramic blade. These attacks are magical for the purposes of overcoming resistance, and deals slashing damage equal to 1d6 plus your attacking ability modifier.
  Full Plating. As an action you can speak the command word to activate the ceramic plating. It grows to cover your entire body, giving you the appearance of an articulated porcelain doll for the next minute. You gain a + 2 bonus to AC and are still considered unarmoured if you were before activating the plating. For the duration, you are vulnerable to bludgeoning damage and gain resistance to fire and slashing damage. Once you use the prosthetic in this manner, you can’t do so again until you complete a short or long rest.